Liver alcohol dehydrogenase (ADH) occurs in human and horse livers in multiple forms, which arise by dimerization of subunits of distinct genetic origin. Liver aldehyde dehydrogenase also occurs in multiple forms whose origin is probably genetic. It is not known whether isoenzymes of either enzyme can be preferentially induced. By dimerization of five genetically distinct subunits sixteen isoenzymes of the human ADH are possible. The inadequacy of the electrophoretic procedures (which separate only five or six isoenzymes) and information about differences in catalytic properties make study of the induction of hyman ADH isoenzymes difficult. Because of species difference in ADH the results from animal studies may not be necessarily applicable to man. This determines the focus of this research on isolation and identification of isoenzymes of human liver ADH to characterize them with respect to various substrates in such a way as to establish means of identification of various isoenzymes in a mixture. In the hope that the isoenzyme status of both ADH and aldehyde dehydrogenase may define the phenotype better, it is proposed to characterize isoenzyme of both ADH and aldehyde dehydrogenase. The aim is to assess the isoenzyme status of both enzymes in a single human liver to make the comparison between different livers more meaningful. By comparison of the isoenzymes of ADH and aldehyde dehydrogenase in alcoholics and non-alcoholics it may be possible to detect any changes which may occur in these two enzymes on excessive ethanol consumption. Work with biopsy samples of human livers from normal and alcoholic subjects which has been already started, employing electrophoresis on starch, will be continued to determine whether any gross changes in ADH isoenzyme pattern occur as a result of prior ethanol consumption.